1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by using a perpendicular magnetic recording system and to a method of manufacturing such a magnetic head.
2. Description of the Related Art
The recording systems of magnetic read/write devices include a longitudinal magnetic recording system wherein signals are magnetized in the direction along the surface of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in the direction orthogonal to the surface of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of implementing higher linear recording density, compared with the longitudinal magnetic recording system.
Like magnetic heads for longitudinal magnetic recording, magnetic heads for perpendicular magnetic recording typically used have a structure in which a reproducing (read) head having a magnetoresistive element (that may be hereinafter called an MR element) for reading and a recording (write) head having an induction-type electromagnetic transducer for writing are stacked on a substrate. The write head comprises a magnetic pole layer that produces a magnetic field in the direction orthogonal to the surface of the recording medium. The pole layer incorporates a track width defining portion and a wide portion, for example. The track width defining portion has an end located in a medium facing surface that faces toward the recording medium. The wide portion is coupled to the other end of the track width defining portion and has a width greater than the width of the track width defining portion. The track width defining portion has a nearly uniform width.
For the perpendicular magnetic recording system, it is an improvement in recording medium and an improvement in write head that mainly contributes to an improvement in recording density. It is a reduction in track width and an improvement in writing characteristics that is particularly required for the write head to achieve higher recording density. On the other hand, if the track width is reduced, the writing characteristics, such as an overwrite property that is a parameter indicating an overwriting capability, are reduced. It is therefore required to achieve better writing characteristics as the track width is reduced. Here, the length of the track width defining portion orthogonal to the medium facing surface is called a neck height. The smaller the neck height, the better is the overwrite property.
A magnetic head used for a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the above-mentioned medium facing surface. The medium facing surface has an air-inflow-side end and an air-outflow-side end. The slider slightly flies over the surface of the recording medium by means of the airflow that comes from the air-inflow-side end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air-outflow-side end of the medium facing surface of the slider. In a magnetic disk drive the magnetic head is aligned through the use of a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit centered on the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt called a skew of the magnetic head is created with respect to the tangent of the circular track, in accordance with the position of the magnetic head across the tracks.
In a magnetic disk drive of the perpendicular magnetic recording system that exhibits a better capability of writing on a recording medium than the longitudinal magnetic recording system, in particular, if the above-mentioned skew is created, problems arise, such as a phenomenon in which data stored on an adjacent track is erased when data is written on a specific track (that is hereinafter called adjacent track erasing) or unwanted writing is performed between adjacent two tracks. To achieve higher recording density, it is required to suppress adjacent track erasing. Unwanted writing between adjacent two tracks affects detection of servo signals for alignment of the magnetic head and the signal-to-noise ratio of a read signal.
A technique is known for preventing the problems resulting from the skew as described above, as disclosed in the Published U.S. Patent Application No. 2003/0151850A1, the Published Unexamined Japanese Patent Application 2003-203311, and the U.S. Pat. No. 6,504,675B1, for example. According to this technique, the end of the track width defining portion located in the medium facing surface is made to have a shape in which the side located backward in the direction of travel of the recording medium (that is, the side located on the air-inflow-end side of the slider) is shorter than the other side. Typically, in the medium facing surface of a magnetic head, the end farther from the substrate is located forward in the direction of travel of the recording medium (that is, on the air-outflow-end side of the slider). Therefore, the above-mentioned shape of the end face of the track width defining portion located in the medium facing surface is such that the side closer to the substrate is shorter than the side farther from the substrate.
As a magnetic head for perpendicular magnetic recording, a magnetic head comprising a pole layer and a shield is known, as disclosed in the U.S. Pat. No. 4,656,546, for example. In the medium facing surface of this magnetic head, an end face of the shield is located forward of an end face of the pole layer along the direction of travel of the recording medium with a specific small space. Such a magnetic head will be hereinafter called a shield-type head. In the shield-type head the shield prevents a magnetic flux from reaching the recording medium, the flux being generated from the end face of the pole layer and extending in directions except the direction orthogonal to the surface of the recording medium. The shield-type head achieves a further improvement in linear recording density.
Reference is now made to FIG. 54 to FIG. 56 to describe an example of a method of forming a pole layer that has a track width defining portion with an end face located in the medium facing surface and having a shape in which a side closer to the substrate is shorter than a side farther from the substrate as described above. FIG. 54 and FIG. 55 each illustrate the end face of the track width defining portion located in the medium facing surface. FIG. 56 is a top view of the pole layer.
In this method, first, a magnetic layer that will be a pole layer 202 later is formed on an insulating layer 201 made of an insulating material such as alumina (Al2O3). Next, an etching mask 203 made of alumina, for example, is formed on the magnetic layer. The etching mask 203 has a plane geometry corresponding to that of the pole layer 202 to be formed. Next, the magnetic layer is etched by dry etching such as reactive ion etching or ion beam etching, using the above-mentioned etching mask 203, so as to form the pole layer 202. In FIG. 54 to FIG. 56 numeral 202A indicates the track width defining portion of the pole layer 202. In FIG. 56 numeral 202B indicates a wide portion of the pole layer 202. ABS indicates the level at which the medium facing surface is formed. NH indicates a neck height.
Next, both side portions of the track width defining portion 202A that are opposed to each other in the direction of the track width are etched by ion beam etching wherein the direction in which ion beams move is tilted with respect to the direction orthogonal to the top surface of the insulating layer 201. Consequently, as shown in FIG. 55, the end face of the track width defining portion 202A located in the medium facing surface is made to have a shape in which the side closer to the substrate (the lower side) is shorter than the side farther from the substrate (the upper side). In FIG. 54 and FIG. 55 the arrows indicate the direction in which ion beams move.
Problems of the above-described method will now be described. First, when the side portions of the track width defining portion 202A are etched by ion beam etching, ion beams are hard to reach portions of the side portions near the bottom of the track width defining portion 202A, and the etching rate is lower in these portions than in the other portion. Moreover, when the side portions of the track width defining portion 202A are etched by ion beam etching, the insulating layer 201 is etched, too, and a substance 204 separated from the insulating layer 201 deposits on the portions of the side portions near the bottom of the track width defining portion 202A.
Because of these reasons, the progress of etching delays in the portions of the side portions of the track width defining portion 202A near the bottom of the track width defining portion 202A. Therefore, it is required to perform ion beam etching for a long period of time so as to make the end face of the track width defining portion 202A located in the medium facing surface have a shape in which the side closer to the substrate is shorter than the side farther from the substrate. However, if ion beam etching is performed for a long period, depressions may be formed in portions of the side portions of the track width defining portion 202A between the lower end and the upper end, as shown in FIG. 55. The broken line of FIG. 55 indicates a desired shape of the track width defining portion 202A. If the above-mentioned depressions are formed in the side portions of the track width defining portion 202A, the volume of the track width defining portion 202A is smaller, compared with the case in which the track width defining portion 202A has the desired shape, and the overwrite property may be thereby reduced.
The neck height NH is made greater than a desired value in some cases if ion beam etching is performed for a long period so that the end face of the track width defining portion located in the medium facing surface has a shape in which the side closer to the substrate is shorter than the side farther from the substrate. This problem will now be described, referring to FIG. 56. In FIG. 56 the broken line with numeral 202D indicates a desired location of the side portion of the wide portion 202B closer to the medium facing surface. If ion beam etching is performed for a long period, the side portion of the wide portion 202B closer to the medium facing surface is etched, too, and the location of the side portion may be farther from the medium facing surface than the desired location. Consequently, the neck height NH is made greater than a desired value. The neck height NH preferably falls within a range of 0.1 to 0.3 μm inclusive, for example, to achieve a good overwrite property. However, even if the pole layer 202 is designed to have such a shape that the neck height NH is 0.1 μm, the neck height NH may be 0.4 to 0.5 μm if ion beam etching is performed for a long period as mentioned above. As thus described, the overwrite property is reduced if the neck height NH is greater than a desired value.
Alternatively, it is possible to form the pole layer 202 by frame plating, instead of forming the pole layer 202 by etching the magnetic layer as described above. In a method of forming the pole layer 202 by frame plating, an electrode film is first formed on the insulating layer 201. Next, a photoresist layer is formed on the electrode film. The photoresist layer is then patterned to form a frame that has a groove having a shape corresponding to the pole layer 202. Next, a current is fed to the electrode film to perform plating so as to from the pole layer 202 in the groove. The frame is then removed. Next, the electrode film except the portion below the pole layer 202 is removed.
Even if the pole layer 202 is formed by frame plating, the above-described problem occurs if both side portions of the track width defining portion 202A are etched by ion beam etching so that the end face of the track width defining portion 202A located in the medium facing surface has a shape in which the side closer to the substrate is shorter than the side farther from the substrate.
Consideration may be given to form the pole layer 202 by frame plating so that the end face of the track width defining portion 202A located in the medium facing surface has a shape in which the side closer to the substrate is shorter than the side farther from the substrate. However, the following problem arises in this case, too. When the pole layer 202 is formed by frame plating, it is required that, after the pole layer 202 is formed, the electrode film except the portion below the pole layer 202 be removed. This removal of the electrode film is performed by dry etching such as ion beam etching. Both side portions of the pole layer 202 are etched, too, when the electrode film is removed. Therefore, if etching is performed to remove the electrode film for a longer period, the pole layer 202 may go out of a desired shape and/or the neck height NH may be greater than a desired value as described above.